Preimplantation embryogenesis in the mouse and rabbit will be studied at the molecular level in order to determine (1) whether pre-programming for the initial stages of embryogenesis occurs during oocyte maturation and (2) the nature of the principal regulatory interactions between blastocystage embryos and the uterine milieu. Protein synthetic patterns will be analyzed in eggs during maturation, and in embryos during the entire preimplantation period, by two-dimensional polyacrylamide gel electrophoresis. The effects of various inhibitors of gene expression will assayed in regard to these protein synthetic patterns and in regard to normal development. Growth regulation in the blastocysts will be studied in terms of processing and nucleo-cytoplasmic transport of ribosomal and messenger RNAs, polysome assembly, and membrane transport systems for various metabolites. BIBLIOGRAPHIC REFERENCES: Van Blerkom, J., S.C. Barton, and M.H. Johnson. (1976) Molecular differentiation in the preimplantation mouse embryo. Nature, 259: 319-321. Van Blerkom, J., and M. Runner. (1976) The fine structural development of preimplantation mouse parthenotes. J. Exp. Zool., 196: 113-124.